1. Field of the Invention
The present invention generally relates to a roll-like printing paper wound around a paper spool, a video printer using such roll-like printing paper and a method of detecting a remaining quantity of a roll-like printing paper. More particularly, this invention relates to a roll-like printing paper having a detection portion formed on a paper spool to detect a rotation of the paper spool wherein the rotation of the paper spool can be detected by the detection portion and a video printer and a method of detecting a remaining quantity of a printing paper in which a rotation of a paper spool of this roll-like printing paper is detected and an alarm is displayed if it is determined based on the detected paper spool rotation that the remaining quantity of the roll-like printing paper approaches to its end.
2. Description of the Related Art
Heretofore, there has been a video printer capable of printing a color image on a printing paper about the size of a postal card. This video printer may use an ink ribbon having a sublimation dye or a molten pigment coated thereon. FIG. 1 shows an example of an ink ribbon using a sublimation dye.
As shown in FIG. 1, this ink ribbon 55 may comprise a ribbon body 56 formed of a belt-like transparent film and thermal dye belts 57 of predetermined length coated (printed) along the longitudinal direction of the ribbon body at a constant interval repeatedly. As the dye belts, there may be generally used yellow (Y) dye belts 57Y, magenta (M) dye belts 57M and cyan (C) dye belts 57C which are complementary colors. A picture change sensor mark 60Y may be formed on a vacant area 58Y provided ahead of the Y dye belt 57Y, and color change sensor marks 60M, 60C may be respectively formed on vacant areas 58M, 58C respectively provided ahead of the M dye belt 57M and the C dye belt 57C.
FIG. 2 is a diagram showing a video printer having an ink ribbon and a printing paper loaded thereon. The ink ribbon 55 of predetermined length may be wound around a supply spool 62, and a tip end thereof may be wound around a take-up spool 63. A roll-like printing paper 71 may be rotatably attached to a printing paper roll presser, not shown, through a paper spool 70. A thermal head 68 serving as a print head and a sensor mark detection means 72 for detecting the sensor marks 60Y, 60M, 60C may be disposed between the pair of spools 62, 63. A platen roller (platen) 69 may be disposed on the opposite side of the thermal head 68 across the ink ribbon 55. The platen 69 may cause the ink ribbon 55 to be urged against the thermal head 68, and may transport the printing paper 71 inserted between the platen 69 and the ink ribbon 55 in cooperation with transport rollers 73, 74.
Such video printer 75 should perceive that the roll-like printing paper 71 approaches to its end after the printing paper was supplied from the platen 69 or the like and the rewinding of the printing paper was finished. To this end, there has hitherto been proposed a method of perceiving the portion near the end of the printing paper 71 by a plurality of detection marks 77 formed near the end of the printing paper 71 as shown in FIG. 3 or a plurality of perforations 78 perforated near the end of the printing paper 71 so as to be detected by an optical sensor as shown in FIG. 4. FIGS. 3 and 4 are diagrams showing the roll-like printing paper from the rear side.
According to the method of perceiving the end of the printing paper by marks provided near the end of the printing paper or by the perforations that can be perceived by the optical sensor, additional manufacturing process such as forming the detection marks 77 on the roll-like printing paper continuously manufactured or forming the perforations 78 that can be perceived by the optical sensor should be required. Unavoidably, there arises a problem that the number of production process increases to lower a production efficiency.
Also, since the whole of the printing paper cannot be used because the printing paper has the portion in which the marks 77 are formed or the perforations 78 are formed, a loss of printing paper may increase. Further, since the end of the printing paper is perceived by the marks or the perforations formed near the end of the printing paper, even though the end of the printing paper can be perceived, a remaining quantity of printing paper could not be perceived in advance.